anubhawm/smart-share

Java Assessment - SmartShare

Assessment Overview

For this assessment, you will be creating a command-line interface application for 'securely' storing files. Files will be uploaded with a 'password'. If another user wants to download the file, they must provide the file name and password in order to download it. The application will be split into two parts - the client and the server. It will have support for concurrency using the Java library's concurrency API and will store files and related information in a relational database.

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Command-line applications

The client side of this application is a command-line application. Command-line applications, also refered to as console applications, are computer programs designed to be used from a text interface, such as a shell. Command-line applications usually accept various inputs as arguments, often referred to as parameters or sub-commands, as well as options, often referred to as flags or switches. Some popular and widely-used command-line applications include grep, git, and curl.

When creating any software that a user will be directly interacting with, it is important to make sure that the 'learning curve' is as smooth and as low as reasonably possible. Making things unique, over-complicated, or going against the grain of the majority of other applications is a great way to ensure that no one will want to use your software. This is especially important for command-line applications. The world of command-line applications is one with a rich history, extensive refinement, and tried and tested standards. Because of this, it is important to follow convention and utilize (as much as possible) what is generally considered best-practices for building CLI applications.

Creating command-line applications is difficult. Parsing text, arguments, options, and providing feedback to the user are just a few of the things you need to consider when writing an easy-to-use command-line application. Like anything in programming, we don't want to re-invent the wheel. We will be using PicoCLI for our client-side java CLI application. It provides an easy-to-use API with minimal boilerplate. Their documentation is fairly good and should be referenced FIRST for issues regarding the CLI portion of this assessment.

Requirements Overview

Concurrency

When a client connects to the server, the server should create a new Thread to handle the request. The thread should run until the response is given to the client.

Uploading

When the user wants to upload a file, they should be required to provide a 'relative path' to the file. They have the option of providing their own password which will act as the 'key' or 'password' for people wishing to download the file. If they do not provide their own password, a password will be generated for them. This functionality is provided for you in the skeleton of the assessment.

File names should be unique. If a file is uploaded with the same name as another file, it should fail to upload.

Additional features for uploading

• Expiration - The client should be able to provide an optional flag denoting the number of minutes until the file expires and can no longer be accessed. If a value is not provided, the expiration should default to 60 minutes from the time the file was uploaded. The maximum value allowed should be 1440 minutes (24 hours) and the minimum value allowed should be 1 minute.
• Maximum Downloads - The client should be able to provide an optional flag denoting the maximum number of downloads available until the file can no longer be accessed. If a value is not provided, there should be no restriction on the number of downloads available.

Downloading

When a user wants to retrieve a file, they will be required to provide a filename and a password.

There are four cases in which the user should not be able to retrieve the specified file.

• The file doesn't exist
• The password doesn't match the password provided when the file was uploaded
• The file has 'expired' - the time has passed that was specified when the file was uploaded
• The maximum downloads have been reached - this value was passed when the file was uploaded

If a download fails, the user should be displayed with the same error message in all cases.

It is up to you where the files are stored once they're downloaded. It is recommended to store them relative to where the application was executed. If run from within eclipse, this will likely be the root of the classpath (the top of the project folder).

File Deletion

If a file is expired or the maximum downloads have been reached, the file entry in the database should be deleted.

Viewing

When a user wants to view a file's current 'summary', they must provide the file name and a correct password. They should then be shown the time created, remaining downloads and time until expiration.

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Provided Skeleton

Disclaimer: The skeleton provided has been briefly tested, but may not be utilizing features of picocli that could make this easier. It is a working example created for the purpose of showing one way to approach this problem. It is written to be enough scaffolding to build on top of as well as demonstrate how to use picocli. However, it is entirely up to you exactly how the user will interact with the CLI as long as the requirements listed below are met. In the case that you are satisfied with the skeleton's implementation, feel free to continue building on top of it.

The skeleton contains a basic boilerplate showcasing some of the basic features of picocli. You are given a skeleton that provides a working command-line interface which has pre-written 'download' and 'upload' commands and their arguments and responds by printing verification message to the console. One of the features that it utilizes is declaratively registered subcommands. This enables the ability to break uploading and download into separate parts of the application without using options. The skeleton contains empty DTO classes in the dto package, an incomplete Api class in the api package, and an empty SmartShareServer class in the server package. The skeleton does not contain any code that connects the client to the server. The server side of the skeleton is left completely empty and it is up to you to create a concurrent server that interacts with a database in order to appropriately store and retrieve files. It also lacks any database connectivity code. You will be required to implement DAO's the do the required CRUD operations on the database tables.

You are also given a schema.sql which you can use to generate an appropriate schema and tables to be used when creating your 'Data Access Objects' classes.

Running/Testing the Client Application

In order to test and run your application, it is recommended to run commands programatically. Examples of this are inside of client/Main.java. The commands that you want to run are provided as arguments to the CommandLine.run method. Each space-separate part of the command that would usually be passed via the command-line should be passed as separate strings.

Examples:

// Run the CLI program with no arguments
CommandLine.run(new SmartShare()); 

// Run the program with the --help flag to see additional usage and documentation for the program
CommandLine.run(new SmartShare(), "-h");

// Run the program with the upload subcommand - will fail due to missing required parameters
CommandLine.run(new SmartShare(), "upload"); 

// Run the program with the upload subcommand and provide a file along with the optional password
// **NOTE** The commandline arguments/flags are passed as *separate* strings
CommandLine.run(new SmartShare(), "upload", "pom.xml", "secretpassword")

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Bonus Challenge

This bonus challenge should only be attempted after completion of all of the above requirements. If any of the above requirements are not met, and the bonus challenge is attempted, you will not receive any extra credit and you will be deducted additional points for attempting extra work without meeting the base requirements.

Modify the schema and application to support uploading/downloading multiple files under a single request. The files should be uploaded with a single password and retrieved with the same password. All other upload/download requirements still apply.